Poiseuille's Law
Enter your known values, leave one input blank, and solves for the missing one. Try different units for next level excitement!
Learning zone
For smooth laminar flow, the throughput of a pipe rises with the fourth power of its radius: double the bore and you pass sixteen times the flow for the same pressure. Nowhere does this matter more than in your arteries — a 10% narrowing costs about a third of the flow, which is why small plaques have outsized consequences and why vasodilation is such a powerful regulator.
The same r⁴ tyranny governs hypodermic needles, inkjet nozzles, and microfluidic chips, where halving a channel's width demands sixteen times the driving pressure.
Poiseuille's Law
Where
- = Volumetric flow rate
- = Pressure drop
- = Pipe radius
- = Dynamic viscosity
- = Pipe length
Missing one of these? Work it out first, then come back
- Volumetric flow rate — Volumetric Flow Rate (Q = Av), Hydraulic Power (P = ρgQh)
- Pressure drop — Valve Flow Coefficient (Cv), Valve Flow Coefficient (Kv, metric)
- Pipe radius — Stokes' Drag (F = 6πμrv), Darcy–Weisbach Head Loss
- Dynamic viscosity — Reynolds Number, Stokes' Drag (F = 6πμrv)
- Pipe length — Darcy–Weisbach Head Loss, Fundamental of a Closed Pipe